BlockFrequency.cpp revision 234353 
1//====--------------- lib/Support/BlockFrequency.cpp -----------*- C++ -*-====//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements Block Frequency class.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Support/BranchProbability.h"
15#include "llvm/Support/BlockFrequency.h"
16#include "llvm/Support/raw_ostream.h"
17#include <cassert>
18
19using namespace llvm;
20
21namespace {
22
23/// mult96bit - Multiply FREQ by N and store result in W array.
24void mult96bit(uint64_t freq, uint32_t N, uint64_t W[2]) {
25  uint64_t u0 = freq & UINT32_MAX;
26  uint64_t u1 = freq >> 32;
27
28  // Represent 96-bit value as w[2]:w[1]:w[0];
29  uint32_t w[3] = { 0, 0, 0 };
30
31  uint64_t t = u0 * N;
32  uint64_t k = t >> 32;
33  w[0] = t;
34  t = u1 * N + k;
35  w[1] = t;
36  w[2] = t >> 32;
37
38  // W[1] - higher bits.
39  // W[0] - lower bits.
40  W[0] = w[0] + ((uint64_t) w[1] << 32);
41  W[1] = w[2];
42}
43
44
45/// div96bit - Divide 96-bit value stored in W array by D. Return 64-bit frequency.
46uint64_t div96bit(uint64_t W[2], uint32_t D) {
47  uint64_t y = W[0];
48  uint64_t x = W[1];
49  int i;
50
51  for (i = 1; i <= 64 && x; ++i) {
52    uint32_t t = (int)x >> 31;
53    x = (x << 1) | (y >> 63);
54    y = y << 1;
55    if ((x | t) >= D) {
56      x -= D;
57      ++y;
58    }
59  }
60
61  return y << (64 - i + 1);
62}
63
64}
65
66
67BlockFrequency &BlockFrequency::operator*=(const BranchProbability &Prob) {
68  uint32_t n = Prob.getNumerator();
69  uint32_t d = Prob.getDenominator();
70
71  assert(n <= d && "Probability must be less or equal to 1.");
72
73  // Calculate Frequency * n.
74  uint64_t mulLo = (Frequency & UINT32_MAX) * n;
75  uint64_t mulHi = (Frequency >> 32) * n;
76  uint64_t mulRes = (mulHi << 32) + mulLo;
77
78  // If there was overflow use 96-bit operations.
79  if (mulHi > UINT32_MAX || mulRes < mulLo) {
80    // 96-bit value represented as W[1]:W[0].
81    uint64_t W[2];
82
83    // Probability is less or equal to 1 which means that results must fit
84    // 64-bit.
85    mult96bit(Frequency, n, W);
86    Frequency = div96bit(W, d);
87    return *this;
88  }
89
90  Frequency = mulRes / d;
91  return *this;
92}
93
94const BlockFrequency
95BlockFrequency::operator*(const BranchProbability &Prob) const {
96  BlockFrequency Freq(Frequency);
97  Freq *= Prob;
98  return Freq;
99}
100
101BlockFrequency &BlockFrequency::operator+=(const BlockFrequency &Freq) {
102  uint64_t Before = Freq.Frequency;
103  Frequency += Freq.Frequency;
104
105  // If overflow, set frequency to the maximum value.
106  if (Frequency < Before)
107    Frequency = UINT64_MAX;
108
109  return *this;
110}
111
112const BlockFrequency
113BlockFrequency::operator+(const BlockFrequency &Prob) const {
114  BlockFrequency Freq(Frequency);
115  Freq += Prob;
116  return Freq;
117}
118
119void BlockFrequency::print(raw_ostream &OS) const {
120  OS << Frequency;
121}
122
123namespace llvm {
124
125raw_ostream &operator<<(raw_ostream &OS, const BlockFrequency &Freq) {
126  Freq.print(OS);
127  return OS;
128}
129
130}
131